U.S. patent application number 14/359021 was filed with the patent office on 2014-11-06 for process and apparatus for molding composite articles.
The applicant listed for this patent is Eric Hurdle. Invention is credited to Eric Hurdle.
Application Number | 20140327187 14/359021 |
Document ID | / |
Family ID | 48428889 |
Filed Date | 2014-11-06 |
United States Patent
Application |
20140327187 |
Kind Code |
A1 |
Hurdle; Eric |
November 6, 2014 |
Process and Apparatus for Molding Composite Articles
Abstract
A method and an apparatus for molding composite articles are
disclosed. The method generally involves the saturation of
reinforcing fibers (e.g. glass fibers, carbon fibers, etc.) with a
matrix (e.g. resin, epoxy, cyanate ester, vinyl ester, polyester,
etc.) in/on a mold using a conventional resin transfer molding
("RTM") process (e.g. "RTM-light") or a vacuum assisted resin
transfer molding ("VARTM") process (e.g. advanced VARTM or
"A-VARTM"), and, once saturation is completed, the vibration of the
matrix-infused fibers using controlled ultrasonic sound waves
transmitted through the mold. By vibrating the matrix-infused
fibers with the ultrasonic sound waves, the method and apparatus
allow voids present between fibers to be closed and localized
pockets of gases to be dislodged and degassed, and also allow the
fibers to compact, thereby producing composite articles with
reduced porosity and higher compaction.
Inventors: |
Hurdle; Eric; (Repentigny,
CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Hurdle; Eric |
Repentigny |
|
CA |
|
|
Family ID: |
48428889 |
Appl. No.: |
14/359021 |
Filed: |
November 19, 2012 |
PCT Filed: |
November 19, 2012 |
PCT NO: |
PCT/CA2012/001069 |
371 Date: |
May 16, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61561521 |
Nov 18, 2011 |
|
|
|
Current U.S.
Class: |
264/443 ;
425/112 |
Current CPC
Class: |
B29C 70/443 20130101;
B29C 35/0261 20130101; B29C 70/54 20130101; B29C 70/44 20130101;
B29C 70/48 20130101; B29C 37/0064 20130101 |
Class at
Publication: |
264/443 ;
425/112 |
International
Class: |
B29C 70/44 20060101
B29C070/44; B29C 70/48 20060101 B29C070/48 |
Claims
1) A process for molding a composite article, the process
comprising: a) placing reinforcing materials into a mold; b)
infusing the reinforcing materials with a matrix; c) transmitting
ultrasounds to the matrix-infused reinforcing materials.
2) A process as claimed in claim 1, wherein the ultrasounds
comprise low frequency ultrasounds and high frequency
ultrasounds.
3) A process as claimed in claim 2, wherein the low frequency
ultrasounds and the high frequency ultrasounds are transmitted
according to a predetermined sequence.
4) A process as claimed in claim 1, wherein the ultrasounds are
transmitted through the mold.
5) A process as claimed in claim 1, wherein the mold comprises at
least one ultrasound transducer mounted thereto or embedded
therein.
6) A process as claimed in claim 1, wherein the process is
performed under vacuum.
7) A process as claimed in claim 1, wherein the process further
comprises placing a vacuum bag over the reinforcing materials and
creating a vacuum between the vacuum bag and the mold.
8) A process as claimed in claim 7, wherein a peel ply layer is
placed between the reinforcing materials and the vacuum bag.
9) A process as claimed in claim 8, wherein an infusion media layer
is placed between the peel ply layer and the vacuum bag.
10) A process as claimed in claim 7, wherein the process further
comprises degassing at least one region of the matrix-infused
reinforcing materials via at least one degassing port located on
the vacuum bag.
11) A process as claimed in claim 7, wherein the process further
comprises degassing several regions of the matrix-infused
reinforcing materials via several degassing ports located on the
vacuum bag.
12) A vacuum-assisted resin transfer molding process for molding a
composite article in a mold, the process comprising transmitting
ultrasounds to resin-infused reinforcing materials located in the
mold.
13) A vacuum-assisted resin transfer molding process as claimed in
claim 12, wherein the ultrasounds comprise low frequency
ultrasounds and high frequency ultrasounds.
14) A vacuum-assisted resin transfer molding process as claimed in
claim 13, wherein the low frequency ultrasounds and the high
frequency ultrasounds are transmitted according to a predetermined
sequence.
15) A vacuum-assisted resin transfer molding process as claimed in
claim 12, wherein the ultrasounds are transmitted through the
mold.
16) A vacuum-assisted resin transfer molding process as claimed in
claim 12, wherein the mold comprises at least one ultrasound
transducer mounted thereto or embedded therein.
17) A vacuum-assisted resin transfer molding process as claimed in
claim 12, wherein the process further comprises degassing at least
one region of the resin-infused reinforcing materials.
18) A molding apparatus for molding a composite article, the
apparatus comprising: a) a mold comprising a top surface and a
bottom surface defining a thickness, and a peripheral edge; b) at
least one ultrasound transducer mounted to mold.
19) A molding apparatus as claimed in claim 18, wherein the at
least one ultrasound transducer is mounted to the bottom surface of
the mold.
20) A molding apparatus as claimed in claim 18, wherein the at
least one ultrasound transducer is embedded in the thickness of the
mold.
21) A molding apparatus as claimed in claim 18, wherein the
apparatus comprises a plurality of ultrasound transducers.
22) A molding apparatus as claimed in claim 18, wherein the
peripheral edge is thicker than the thickness of mold.
23) A molding apparatus as claimed in claim 18, further comprising
a support frame supporting the mold.
24) A molding apparatus as claimed in claim 23, wherein the mold is
suspended on the support frame.
25) A molding apparatus as claimed in claim 24, wherein the mold is
suspended on the support frame via at least one vibration
isolator.
26) A molding apparatus as claimed in claim 18, further comprising
a vacuum bag.
27) A molding apparatus as claimed in claim 26, wherein the vacuum
bag comprises at least one degassing port.
28) A molding apparatus for molding a composite article with a
vacuum assisted resin transfer molding process, the apparatus
comprising: a) a mold comprising a top surface and a bottom surface
defining a thickness, and a peripheral edge; b) at least one
ultrasound transducer mounted to mold.
29) A molding apparatus as claimed in claim 28, wherein the at
least one ultrasound transducer is mounted to the bottom surface of
the mold.
30) A molding apparatus as claimed in claim 28, wherein the at
least one ultrasound transducer is embedded in the thickness of the
mold.
31) A molding apparatus as claimed in claim 28, wherein the
apparatus comprises a plurality of ultrasound transducers.
32) A molding apparatus as claimed in claim 28, wherein the
peripheral edge is thicker than the thickness of mold.
33) A molding apparatus as claimed in claim 28, further comprising
a support frame supporting the mold.
34) A molding apparatus as claimed in claim 33, wherein the mold is
suspended on the support frame
35) A molding apparatus as claimed in claim 34, wherein the mold is
suspended on the support frame via at least one vibration
isolator.
36) A molding apparatus as claimed in claim 28, further comprising
a vacuum bag.
37) A molding apparatus as claimed in claim 36, wherein the vacuum
bag comprises at least one degassing port.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] The present patent application claims the benefits of
priority of U.S. Provisional Patent Application No. 61/561,521,
entitled "Apparatus and Method for the Controlled Ultrasonic Resin
Infusion of Composite Articles" and filed at the United States
Patent and Trademark Office on Nov. 18, 2011, the content of which
is incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention generally relates to the field of
resin transfer molding ("RTM") processes and vacuum assisted resin
transfer molding ("VARTM") processes used for molding composite
articles, and more particularly relates to advanced vacuum assisted
resin transfer molding ("A-VARTM") processes.
BACKGROUND OF THE INVENTION
[0003] There are many industries producing fiber-reinforced resin
composite parts. For instance, composite parts are commonly used in
the automotive, marine, industrial, and aerospace industries.
[0004] Depending on the requirements of each industry, various
methods and processes can be used to produce composite parts. One
commonly known method is the resin transfer molding ("RTM") process
in which reinforcing materials (e.g. glass fibers, carbon fibers,
etc.) are placed into a closed mold and then impregnated at high
pressure (e.g. 400 psi and higher) with a liquid matrix (e.g. a
polymer resin). In a variant of the RTM process, the closed mold is
put under vacuum prior to the injection, at atmospheric pressure,
of the matrix to impregnate the reinforcing materials. Such a
process is generally known as a vacuum assisted resin transfer
molding ("LIGHT RTM") or ("VARTM") process. In line with the VARTM
process is the advanced VARTM ("A-VARTM") process. In A-VARTM
process, the mold is usually open and light weight compared to
other RTM or VARTM processes. To compress the layers of
reinforcement materials on a complex mold shape, a flexible vacuum
bag is used. When the bag is put under vacuum, the atmospheric
pressure insures the proper compaction of the reinforcing materials
and removes air in the bag. After impregnation of the reinforcing
fibers with the matrix, the pressure on the bag becomes neutral and
degassing become difficult.
[0005] One of the problems of composite parts made from VARTM
processes is the porosity. Indeed, despite due care, the
impregnation of the reinforcing materials with the matrix is never
perfect and the resulting composite part typically contains
porosities such as voids and gas bubbles around fibers and in the
matrix. Though porosities are generally not a major problem in the
automotive and marine industries, they are a significant problem
for the aerospace industry. Indeed, in the aerospace industry, the
porosity content of a composite part must be severely controlled to
prevent its failure.
[0006] Unfortunately, current RTM, VARTM, even A-VARTM processes
are not able to produce composite parts with the requisite limited
amount of porosities suitable for the aerospace market.
[0007] To overcome the shortcomings of VARTM processes, the
aerospace industry currently produces composite parts using a
specific process, sometimes referred to as pre-preg, using
reinforcing materials pre-impregnated with a resin matrix and ready
to be vacuum bagged and cured at high temperature (e.g. 130.degree.
C. and higher) in a pressurized autoclave. The main advantage of
autoclaved pre-impregnated composite parts is the almost complete
absence of voids and porosities (typically less than 1%). However,
the pre-impregnated process is excessively expensive. For instance,
pre-impregnated reinforcing materials must be stored at -18.degree.
C. or colder to slowdown the cure cycle of pre-mixed resin, they
have to be thawed many hours before usage and they need significant
supervision. In addition, the pre-impregnated process requires a
pressurized autoclave which is very expensive, particularly for
large composites parts.
[0008] Hence, there is a need for an improved A-VARTM process and
associated molding apparatus which could mitigate at least some
shortcomings of prior art VARTM processes and which could be able
to produce composite parts and articles with a porosity level
similar or better to the pre-impregnated process.
SUMMARY OF THE INVENTION
[0009] The shortcomings of prior art methods and processes for
molding composite articles using RTM, VARTM, or A-VARTM processes
are at least mitigated by submitting the resin-infused reinforcing
materials to ultrasonic sound waves.
[0010] Hence, a typical process to produce resin-infused composite
articles in accordance with the principles of the present invention
generally comprises the placement of reinforcing materials (e.g.
glass fibers, carbon fibers, etc.) in or on a mold, the infusion,
typically under vacuum, of the reinforcing materials with a matrix
(e.g. a resin), and, once the infusion is completed and before the
end of gel time, the transmission of controlled ultrasonic sound
waves to the resin-infused reinforcing materials through the
mold.
[0011] For its part, a molding apparatus in accordance with the
principles of the present invention generally comprises a mold
having a molding surface, and an infusion vacuum bag configured to
cover the reinforcing materials during the infusion and apply
pressure thereon. In accordance with the principles of the present
invention, the mold comprises at least one though typically several
ultrasound transducers mounted to the mold and/or embedded within
its thickness.
[0012] The ultrasonic sound waves are used to vibrate the
reinforcing materials via the mold when their reinforcing fibers
are saturated with resin. By vibrating the reinforcing materials,
it is possible to eliminate or at least significantly reduce voids
and bubbles present in and around the resin-infused reinforcing
materials and thereby reduce the level of porosity in the final
molded composite article and getting a better compaction of the
fibers.
[0013] Since RTM, VARTM, A-VARTM processes can be used with
different types of polymer resin matrices, reinforcing materials,
and molds, the mold will typically comprises different ultrasonic
transducers typically able to operate at different frequency
ranges. The choice of the ultrasonic transducers will typically be
based on the type of matrices and reinforcing materials used, and
on the mold types and shapes. In addition, the position of each of
the transducers on or embedded in the mold is typically determined
to provide proper vibration of the resin-infused reinforcing
materials.
[0014] In typical yet non-limitative embodiments, various
ultrasonic frequency ranges are used to vibrate the resin-infused
reinforcing materials. In some of these embodiments, the different
ultrasonic frequency ranges can be transmitted at different times
according to a predetermined sequence, and/or at different levels
of power. For instance, high frequency ultrasonic sound waves (e.g.
170 kHz to 200 kHz, at 25 W) could be transmitted to generally
vibrate the reinforcing fibers and thus close voids present between
fibers, followed, or preceded, by low frequency ultrasonic sound
waves (e.g. 27 kHz to 40 kHz, at 25 W) to fill and/or fraction
bubbles present in the resin. Other ultrasonic frequencies can
however be used.
[0015] In typical yet non-limitative embodiments, the vacuum bag of
the molding apparatus comprises additional degassing vacuum ports
strategically positioned on the bag (depending on the shape and
size of the mold) for maximizing local degassing and specific
bleeding of matrix used in the process.
[0016] Notably, the process and related molding apparatus in
accordance with the principles of the present invention allow the
molding of composite articles and parts having a much higher
compaction of fibers due to the vibration of the reinforcing fibers
when saturation is completed, i.e. when the reinforcing material
fibers are wet (notably, dry fibers would damp vibrations and not
provide results). Using such a process and its related molding
apparatus, the ratio matrix/fibers potential (e.g. 70% and higher)
can be very high without creating dry spots, allowing the
manufacturing of composite articles and parts which meet the
stringent porosity level and high ratio of matrix/reinforcement
fiber of the aerospace industry at a much lower cost than
pre-impregnated or pre-preg processes.
[0017] Other and further aspects and advantages of the present
invention will be obvious upon an understanding of the illustrative
embodiments about to be described or will be indicated in the
appended claims, and various advantages not referred to herein will
occur to one skilled in the art upon employment of the invention in
practice. The features of the present invention which are believed
to be novel are set forth with particularity in the appended
claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0018] The above and other aspects, features and advantages of the
invention will become more readily apparent from the following
description, reference being made to the accompanying drawings in
which:
[0019] FIG. 1 is schematic flow-chart of a process for molding
composite articles in accordance with the principles of the present
invention.
[0020] FIG. 2 is a cross-sectional side view of a molding apparatus
for molding composite articles in accordance with the principles of
the present invention.
[0021] FIG. 2A is an enlarged partial cross-sectional side view of
the molding apparatus of FIG. 2.
[0022] FIG. 3 is a cross-sectional side view of the mold of the
molding apparatus of FIG. 2, mounted to a support frame.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0023] A novel process and related apparatus for molding composite
articles will be described hereinafter. Although the invention is
described in terms of specific illustrative embodiments, it is to
be understood that the embodiments described herein are by way of
example only and that the scope of the invention is not intended to
be limited thereby.
[0024] Referring first to FIG. 1, a flow-chart depicting an
embodiment of a process 100 to mold composite articles in
accordance with the principles of the present invention is
shown.
[0025] In the present embodiment, the process 100 is mostly based
on a A-VARTM process. Hence, the process 100 typically comprises
the placement of reinforcing materials on a mold which is in the
shape of the desired article (at 102). In the present embodiment,
several types of reinforcing materials can be used. For instance,
glass fibers, carbon fibers, glass fiber fabric, carbon fiber
fabric, etc.
[0026] Next, once the reinforcing materials are properly positioned
on the mold, a vacuum bag (or vacuum film) is disposed over the
reinforcing materials, a vacuum pump is connected to the vacuum
port of the bag and a matrix source is connected to the matrix port
(at 104). At this point, the molding apparatus is ready for the
injection of the matrix.
[0027] Then, the vacuum pump is turned on to create a full vacuum
(e.g. .about.25 in Hg or higher) in the vacuum bag. Understandably,
as the vacuum is created inside the vacuum bag, atmospheric
pressure will press the bag against the reinforcing material. At
the same time, the resin matrix is introduced into the bag via the
matrix port for infusing the reinforcing materials (at 106).
[0028] Understandably, as the matrix is introduced in the bag under
vacuum, the matrix will tend to fill most of the empty areas and
voids in and around the reinforcing materials.
[0029] Once the reinforcing materials is properly infused and
saturated with resin, ultrasonic sound waves are transmitted to the
resin-infused reinforcing materials (also referred to as a
laminate) through the mold (at 108). Some of the high-frequency
ultrasonic sound waves will cause the vibration of the fibers of
the reinforcing materials, allowing voids which naturally occur
between fibers to be closed, thereby increasing the overall the
compaction of the laminate. Also, some low-frequency ultrasonic
sound waves will cause gas bubbles to be filled-up and/or
fractioned to be ultimately degassed by the vacuum and degassing
port(s).
[0030] As it will be described in more details below, in the
present embodiment, the ultrasonic sound waves can be transmitted
at different frequencies and/or power levels according to one or
more predetermined sequences.
[0031] After the transmission of the ultrasonic sound waves, the
laminate is left to cure at room temperature for a predetermined
amount of time (at 110). In the present embodiment, the curing of
the laminate is performed under vacuum.
[0032] Optionally, the laminate can be subjected to a
high-temperature post cure to generally improve the thermal and
mechanical properties of the laminate (at 112).
[0033] Finally, the laminate is demolded and trimmed or machined to
remove excess materials and/or other surface imperfections (at
114). The laminate is then a finished composite article or
part.
[0034] Referring now to FIGS. 2 and 2A, an embodiment of a molding
apparatus 200 to enable the molding process is depicted. The
apparatus 200 typically comprises a mold 210, typically made of
composite material or metallic material, and a vacuum bag 230
typically made from a thin silicone membrane or nylon bagging film
(e.g. Airtech Wrightlon 5400).
[0035] In the present embodiment, to provide a uniform rough
surface finish on the bag side of the molded composite part, a
nylon peel ply 240 (e.g. Airtech econostitch) is disposed over the
reinforcing materials 302 prior to the installation of the vacuum
bag 230. Also, in the present embodiment, an infusion media layer
250 (e.g. Airtech green flow 75) is disposed between the peel ply
240 and the vacuum bag 230 to allow the resin matrix to freely flow
during its injection (see FIG. 2A).
[0036] As shown in FIG. 2, the mold 210 comprises a top surface 212
and a bottom surface 214 defining a thickness 216. The top surface
212 provides a molding surface for receiving the reinforcing
materials 302. Understandably, the top surface 212 of the mold 210
is generally in the shape of the article or part to be molded.
Hence, the top surface 212 is shown as flat for illustration
purpose only.
[0037] For its part, the vacuum bag 230 comprises at least one
resin inlet port 232 allowing the resin to enter in the bag 230
during the infusion of the reinforcing materials 302, and at least
one vacuum outlet port 234 allowing a vacuum to be created inside
the bag 230 prior and during the infusion. The vacuum outlet port
234 is typically connected to a vacuum source (e.g. .about.25 in Hg
or higher) such as a vacuum pump (not shown). Understandably, when
a vacuum is created inside the bag 230 which is made from flexible
material, the bag 230 collapses and applies pressure on the
resin-infused reinforcing materials 302.
[0038] To allow the removal of air and other gas bubbles around the
fibers and from the resin-infused reinforcing materials 302, the
vacuum bag 230 comprises at least one though typically several
degassing vacuum outlet ports 236. Typically, these degassing
vacuum outlet ports 236 are strategically positioned on the vacuum
bag 230 to provide proper degassing of the resin-infused
reinforcing materials 302. Local degassing ports allow to degas
specific area(s) or region(s) and also allow to bleed extra matrix
at specific location(s) to reach a maximum of fiber volume fraction
(ratio fiber/resin) without creating dry spots.
[0039] To prevent the vacuum bag 230 from leaving a shinny finish
and/or from adhering on the resin-infused reinforcing materials 302
during the molding process, the layer of peel ply cloth 240 is
disposed on reinforcement material 302 between the media fusion
layer 250 and resin-infused reinforcing materials 302. This cloth
240 is typically removed once the cure and/or post cure of the part
is completed.
[0040] Also shown in FIG. 2, in accordance with the principles of
the present invention, the mold 210 comprises at least one
ultrasonic sound wave transducer 218 mounted to its bottom surface
214 or embedded into its thickness 216. In FIG. 2, two transducers
218 are shown. Embedded transducers such as transducer 218A are
typically used for thin composite parts (e.g. .about.0.0125'')
whereas surface-mounted transducers such as transducer 218B are
typically used for thicker composite parts (e.g. 0.0125'' up to
0.500'').
[0041] Embedded transducers are typically piezoelectric transducers
made of ceramic flat disk. Such transducers are typically custom
made by APC International, Ltd.
[0042] Surface-mounted transducers are typically Langevin type
transducers. Such transducers are typically made of an aluminum
base and a head made of two bonded piezo-disks. Such transducers
are made, for instance, by Cleaning Technologies Group
(Blackstone-NEY Ultrasonics).
[0043] As shown in FIG. 2, in the present embodiment of the molding
apparatus 200, the region 222 of the bottom surface 214 located
underneath the embedded transducer 218A is made thicker. By making
the region 218 thicker (typically about the thickness of the
transducer 218A), the vibrations 205 generated by the transducer
218A which travel downwardly and away from the resin-infused
reinforcing materials 302, are at least partially reflected back
toward the resin-infused reinforcing materials. Hence, the thicker
region 222 typically reduces energy losses.
[0044] Also, in the present embodiment of the molding apparatus
200, the surface-mounted transducer 218B is mounted (e.g. bond or
bolted) to a metallic plate 224 (e.g. an aluminum plate) itself
mounted to the bottom surface 214 of the mold 210. Such plate 224
is used to avoid the mounting of the transducer directly to the
mold 210 and to allow the easy replacement of the transducer 218B
if necessary. In addition, in a manner similar to region 222, the
region 226 around the plate 224 is also typically made thicker
(about the thickness of the plate 224).
[0045] Understandably, the transducers 218 are connected to an
ultrasound generator (not shown). An ultrasound generator that has
provided satisfactory results is the Multisonic
40-80-120-140-170-220-270-MSG2-12 t2-230V made by Blackstone-NEY
Ultrasonics.
[0046] To promote the vibration of the fibers of the reinforcing
materials and to allow the bubbles to collapse or fraction,
sequences of ultrasounds are typically transmitted.
[0047] An exemplary sequence that has shown satisfactory results is
a follows: 40 kHz for about 15 seconds, 170 kHz for about 15
seconds, 40 kHz for about 10 seconds, 200 kHz for about 5 seconds,
170 kHz for about 15 seconds, and so on as needed. Understandably,
different resin matrix, reinforcing materials and mold shapes might
warrant different sequences, different duration, different power
levels and/or different frequencies.
[0048] When high frequencies are used (e.g. 170 kHz to 200 kHz),
the heat produced by the vibration of the fibers has shown to
reduce the gel time significantly if used too often (e.g. for more
than 60 seconds straight). Depending on the matrix and reinforcing
materials used, frequency sequences and time exposure will
change.
[0049] Since the ultrasonic sound waves transmitted to the
resin-infused reinforcing materials are effectively transmitted
through the mold 210, it is advantageous to have the mold 210 able
to freely vibrate in order to benefit, among other things, from
constructive interferences between the main vibrations and the
returning ones. Using constructive interferences can allow the use
less powerful sources of ultrasounds. To allow the mold 210 to
vibrate, it can be suspended on a frame 260 via passive suspension
elastomeric vibration isolator 262 (e.g. Newport
Vibration-Isolator). FIG. 3 shows an example of the mold 210
suspended on the frame 260 via the suspensions (or isolators) 262.
For a range of ultrasounds frequencies of 40 to 200 kHz, it has
been found that the suspension 262 can be also made of a hard
rubber, e.g. of 50 to 70 Shore or can be a mini air suspension.
[0050] In the present embodiment, the edges 220 of the mold 210 are
thicker than the thickness 216 of the mold 210, typically about
twice as thick. The thicker edges 220 allow the vibrations moving
outwardly to be reflected back inwardly, thereby preventing or at
least reducing energy losses.
[0051] When the mold 210 vibrates, standing waves will likely occur
and have the advantage of high amplitude resulting from
constructive interferences. However, the stationary status of these
standing waves can also create patterns of porosity since some
regions of the resin-infused reinforcing materials 302 may vibrate
more, or less, than other regions.
[0052] In order to prevent stationary standing waves, displacement
of the standing waves can be achieved by a sweeping frequencies
produced by the ultrasound generator. For instance, sweeping lower
frequencies will help move the standing waves by creating
disturbance.
[0053] Typically, the ultrasonic sound waves will not shake the
mold 210 but will travel through the mold 210 and only vibrate the
resin-infused reinforcing materials 302. Notably, it has been found
that the amount of power needed to properly vibrate the
resin-infused reinforcing materials 302 will be lowered if the
vibrations are chosen to match the natural resonance frequency of
the mold 210. If the vibrations are not chosen to match the natural
resonance frequency of the mold 210, more power may be necessary
and the performances would possibly be affected.
[0054] The natural resonance frequency of the mold 210 can be
obtained via different methods. One method involves the use of a
laser interferometer. In such method, the mold 210 is suspended and
then knocked at the location where the transducer 218 is intended
to be installed. Then the mold 210 is let vibrating and the
vibration pattern is measured with the interferometer. The position
of the transducer 218 can then be fine-tuned in order to obtain the
desired vibration pattern. The method is then repeated for each
transducer 218 to obtain proper match and coverage
performances.
[0055] With the proper equipment selected and installed on the
molding apparatus, the process will provide satisfactory
results.
[0056] Below is an example of a process performed in accordance
with the principles of the present invention.
[0057] First, the mold surface is prepared with a liquid release
agent (e.g. Zyvax) and vacuum bag sealant tape (e.g. Airtech
AT200Y) is applied on the flanges of the mold.
[0058] Then, the reinforcing material plies are laid-up directly on
the mold surface and the peel ply layer, the media infusion layer
and the vacuum bag are sequentially disposed over the reinforcing
material plies. The vacuum bag is connected to the resin matrix
source and to the vacuum pump.
[0059] Then, the vacuum pump is turned on to create the vacuum
inside the vacuum bag. Several checks are typically performed to
make sure that there are no leaks.
[0060] At this point, the resin matrix is injected into the mold
via the vacuum bag to infuse the reinforcing material plies. As
soon as the reinforcing material plies are thoroughly saturated
with resin matrix, the transmission of ultrasonic sound waves is
started.
[0061] At first, low frequency ultrasounds (e.g. about 40 kHz) and
high frequency ultrasounds (e.g. about 170 kHz-200 kHz should be
the maximum range) are alternatively transmitted for about 10 to 15
seconds each to chase voids and bubbles. During the transmission of
the ultrasounds, larger bubbles are going to surface and be
degassed while microscopic bubbles are going to be fractioned into
still smaller bubbles or will agglutinated together into larger
bubbles and be degassed.
[0062] At this point, one or more of the degassing ports are
slightly opened to allow localized zone(s) (e.g. sharp corners) to
evacuate gases. However, it is important to prevent the resin
matrix to flow into the degassing ports.
[0063] Once the resin matrix no longer shows signs of degassing,
the ultrasound transmission cycle is modified so that the high
frequency ultrasounds (e.g. about 170 kHz) are transmitted for a
longer period, about 15 to 25 seconds, and the low frequency
ultrasounds (e.g. about 40 kHz) are transmitted for a shorter
period of time, about 5 to 10 seconds.
[0064] The modified cycle is used to vibrate the fibers of the
reinforcing material plies and keep degassing. In that sense, there
will typically be traces of degassing at the surface of the resin
matrix when the fibers move and compact and cause microscopic
bubbles surrounding the fibers to detach.
[0065] Then, again, one or more of the degassing ports are slightly
opened to allow the evacuation of the gases. When the degassing
ports are opened, it is important to prevent the resin matrix to
flow in them.
[0066] When the degassing is completed, the resin matrix can be
bled if needed. To do so, the degassing vacuum ports are gently
opened to allow some resin matrix to fill the tubes (about 1% of
the total extra resin matrix) and then closed to allow the resin
matrix to flow in dryer spots and equilibrate. This operation can
be repeated as needed. Notably, the amount of extra matrix allowed
in the degassing vacuum ports tubes should be calculated at the
beginning of the infusion process and collected in the tubes or in
a catch pot if the quantity is large. The resin matrix should be
left to equilibrate for a period of time (e.g. 30 seconds) after
the last bleeding cycle before turning off the ultrasounds.
[0067] Understandably, the matrix used in the above process should
have a long enough gel time to allow the different steps of the
process to be performed properly. In that sense, when the fibers of
the reinforcing material plies vibrate because of the ultrasounds,
they absorb an important quantity of energy which is released in
part as heat. This heat can cause the gel time of the matrix to be
affected, sometimes significantly.
[0068] Notably, once the jellification of the resin matrix has
begun, the transmission of ultrasounds shall stop to prevent
irreversible fractures of the matrix and/or of the reinforcement
fibers. Understandably, a hardened matrix will resist vibrations
and could present micro fragmentations which will affect the
structural integrity of the finished composite article or part.
[0069] Once the process is well controlled, some steps could be
made with the assistance of a computer.
[0070] By using a molding apparatus and executing a process in
accordance with the principles of the present invention, it is
possible to eliminate or at least significantly reduce the void
content and porosity while the matrix is in liquid phase. Composite
parts and articles made with a molding apparatus and a process in
accordance with the principles of the present invention are of very
high quality (e.g. aerospace-grade) and can compare with composite
parts and articles made using prepreg in an autoclave.
[0071] While illustrative and presently preferred embodiments of
the invention have been described in detail hereinabove, it is to
be understood that the inventive concepts may be otherwise
variously embodied and employed and that the appended claims are
intended to be construed to include such variations except insofar
as limited by the prior art.
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